(a) Technical Field
The present invention relates to a cement-free high strength unshaped refractory, in which barium aluminate and a dispersant are further added to a refractory which includes a refractory material containing Al2O3 and SiC and an alumina sol binder to largely improve handling molding strength of the unshaped refractory. The unshaped refractory according to the present invention is usefully applicable to a lining which contacts slag in a blast furnace or a gasifier.
(b) Background Art
Unshaped refractories are in general preferred over refractory bricks due to the gaps present between refractory bricks. However, unshaped refractories have disadvantages that they require a longer lifespan, variety in material selection, and improvement in construction methods.
The unshaped refractories generally consist of refractory materials composed of oxides, carbides, or mixtures thereof, and a binder for binding the refractory materials. As the binder included in the refractory, a calcium aluminate cement binder is mainly used, but the cement binder has a long dry time due to slow water evaporation. In addition, the cemented binder, due to the presence of calcium oxide (CaO), lowers the viscosity of slag by reacting with it at high temperature, thus readily facilitating permeation into the refractory and accelerating their erosion. Consequently, as an inorganic binder to be included in the refractory, a low-calcium aluminate cement with low calcium content is preferred.
Recently, a phosphate unshaped refractory has been suggested to replace the cement binder. The phosphate unshaped refractory uses mono-aluminum phosphate as a binder, and uses magnesium oxide (MgO) as a hardener. Although the phosphate unshaped refractory is applicable in a combustion furnace, it is not suitable for a gasifier with insufficient oxygen. Moreover, in a P2O5—MgO-based unshaped refractory, a compound with low melting point is generated, and mono-aluminum phosphate, which is water-soluble, moves to the surface, resulting in non-uniform strength. Under high temperature reduction atmosphere, P2O5 is volatilized so that the strength can be lowered or become non-uniform. Therefore, the phosphate unshaped refractory is not suitable for forming a refractory structure.
Recently, an unshaped refractory using a hydratable alumina binder has been introduced. The hydratable alumina mainly includes α-alumina powder, and also includes ρ-alumina which readily reacts with water, and a small amount of CaO and SiO2. Examples of currently commercialized hydratable alumina binders may include AlphaBond 300 and 500 of Almatis Alcoa Industrial Chemicals Division. Alphabond 300 has the average particle size of 2.3 μm, and CaO content of less than 0.1 wt %. Alphabond 500 has the average particle size of 5.2 μm, and CaO content of 0.6 wt %. Alphabonds are recommended for use in no-cement castables, with binder content in the range of 3-7 wt %. However, a refractory using a hydratable alumina binder has a low strength (1.2-2.0 MPa) at a temperature from 800 to 1200° C., where dehydration occurs but no binding between refractories occurs.
In addition, Japanese Patent Application Publication No. 2004-168580 discloses a SiC-containing unshaped refractory used for lining of a blast furnace by including an alumina cement binder in a refractory containing Al2O3 and SiC. That is, the unshaped refractory is manufactured using SiC fine powder (<5 μm), alumina (<1 μm), silica (<1 μm) and a small amount of alumina cement (1.5%), and an SiC content of less than 5 μm is 3-10 wt %, and improvements are obtained in terms of fluidity, erosion resistance, and abrasion resistance.
In addition, the present inventors have already disclosed an unshaped refractory including refractory materials; which contains Al2O3 and SiC, and an alumina sol binder in Korean Patent Application Publication No. 10-2011-0104713. The use of alumina sol binder facilitates easy contact between the refractory materials due to fluidity of the sol, thus improving the binding property. Moreover, since the cement binder is not used, the problem associated with the use of cement is solved, and a thin film is formed with gelation of the alumina sol thereby enabling a quick dry and generation of no crack during the dry process.
However, when compared to a refractory using a conventional cement binder or phosphate-based binder, like a hydratable alumina binder the disclosed unshaped refractory has low green strength(okay), and therefore, there is a need for the development of a technique for improving handling strength.